The contractor sought more money because of the additional strengthening work required on the main roof truss to support the new roof.
Balfour Beatty was awarded a £154m contract in January 2014 to transform the former Olympic Stadium, which included installing the largest single span cantilever roof in the world, constructing the warm-up track, spectator and hospitality facilities, and external landscaping.
The converted stadium will host five matches during the 2015 Rugby World Cup 2015 and be the permanent home of West Ham United Football Club from 2016.
A statement from the client body, Queen Elizabeth Olympic Park, which comes under the Mayor of London’s office, said: “This is a unique two year transformation project and a hugely complex engineering scheme, using techniques previously employed on oil rigs. Providing adequate support for the new roof has required significantly more strengthening work to the main roof truss, which was originally designed to be taken down after the Games. We have therefore today agreed to increase the value of the Balfour Beatty contract by £35.9m to £189.9m.”
It added: “We will meet these costs from the project contingencies and additional income we will generate from our other developments. There will therefore be no additional call on the taxpayer and no impact on our current programme. We will continue to deliver the most successful Olympic legacy in the history of the Games. We are committed to creating a new heart for east London with new jobs and homes, alongside iconic sporting venues and beautiful parklands.”